The present invention relates to a golf ball molding die and a golf ball manufactured by using the golf ball molding die. More particularly, it relates to an improvement of a die used for molding a golf ball.
A golf ball is usually manufactured by an injection molding process or a compression molding process. In the both cases of these processes, a molding die is used. In this injection molding die, a spherical cavity is formed.
When a golf ball is molded, air that is present in a gap between the wall surface of the cavity and a rubber-made elastic body, which is a core material of the golf ball, and a gas released mixedly with a resin are discharged to the outside of the die through a gap between a vent pin accommodating hole provided in the wall surface of the cavity and a vent pin.
If the air and gas are not discharged well from the die, a defect is formed on the surface of the golf ball, e.g., what is called a weld-mark such as a bird footprint is formed on the surface of the product. To prevent such a defect, measures can be taken by increasing the number of installed vent pins. However, a plurality of support pins must be provided in the wall surface of the cavity to hold the core material, and also a plurality of protrusions for forming dimples must be arranged on the whole wall surface of the cavity, so that the number and positions of installed vent pins are restricted.
Japanese Patent Application Publication No. 2000-37480 describes a die in which the vent pin is formed of a porous material. Also, Japanese Patent Application Publication No. 7-80848 describes a die in which venting slits are provided in the wall surface of the cavity. When the gas is discharged, a minute amount of resin contained in the gas solidifies, so that a mold deposit is produced. The mold deposit produced in the porous vent pin or in the slit cannot be removed easily by cleaning etc., so that the venting performance is not restored.
U.S. Pat. No. 6,877,974 describes a vent pin that is formed by dividing the vent pin into two sections in the lengthwise direction of pin and by assembling the two pin sections each having a semicircular cross section into one vent pin having a circular cross section. On the mating surface between the two pin sections, a concavity forming an air outlet is provided. In this patent, the size of a venting opening capable of being provided per unit area of the tip end of pin is restricted.